The present invention relates broadly to disinfection of root canals during endodontic, or root canal, procedures, and in particular to the use of micro-bubbles which when mechanically activated, for example, with ultrasonic/sonic energy improve the micro-bubble pulsations/interaction with the root canal wall (mechanical effect) and simultaneously enhance the efficacy of light activated disinfection (antibacterial effect).
Apical periodontitis is defined as an inflammatory process around the tooth root-apex, and is primarily a sequel to microbial infection (mainly bacteria) of the root-canal space of the tooth. Infection of the root canal and associated regions of tooth, generally known as root canal infection/endodontic infection, is a widespread problem all over the world. It represents a localized infection where bacteria have been recognized as the main etiological agent. The clinical manifestation of the disease is due to the combined action of microorganisms and host immune response.
The main objective of the clinical management of apical periodontitis (root canal infection) is to eliminate bacteria from the root canal system. If the periodontitis cannot be managed, the tooth will be lost and will need to be extracted. Traditional root canal treatment (RCT) aims to disinfect the root canal by removing the infected tissue and the disease causing bacteria by means of ‘chemo-mechanical’ preparation. Complete disinfection of the root canal is rarely achieved, although in most cases the disease symptoms recede.
There are several constraining factors in root canal disinfection. The first is the bacterial biofilm itself. The biofilm, comprised of bacteria and their products, covers the root canal wall and fills the dentinal microtubules. The biofilm (especially the biofilm in the microtubules) thus can be difficult to target chemically or to mechanically disrupt effectively. Chemicals, such as sodium hypochlorite are fairly effective at disinfecting the root canal. However, sodium hypochlorite can react with tissue remnants and the dentin in the canal, and can adversely affect the canal if left in the canal for too long. Thus, the longer duration required to effectively disinfect the canal must be weighed against the effect the sodium hypochlorite will have on the tooth structure. Other factors include the dentinal tubules, the dentin composition, and the complexities of the root canal structure itself.
The success rate of root canal treatment has generally been regarded as high, on the order of 87% (Eriksen H M, 1998). This figure applies to root canal treatment carried out by a specialist, where a higher expertise would result in a better technical standard of treatment, whereas the success rate in general practice is on the order of 72%. Failure of conventional treatment is mostly due to the persistence of bacterial population even after chemo-mechanical disinfection. Limitations in conventional treatment procedures are attributed to its inability to reach bacterial biofilm, especially in anatomically inaccessible regions of tooth. The presence of biofilms, which is the surface adsorbed growth of microorganism, has been associated with chronic human infections (Costerton J W et al, 1994; Parsek M R and Singh P K, 2003). This is because bacteria growing biofilms are highly resistant to conventionally used antimicrobial regimes, due to the biochemical composition of biofilm matrix and altered physiology of bacteria residing in biofilms (Parsek M R and Singh P K, 2003).
In traditional root canal therapy (RCT), the root canal is initially shaped by an instrumentation procedure (with root canal reamers and files) and then cleaned using root canal irrigants (liquid chemicals) and disinfected using medicaments to achieve a “bacteria free” root canal system. The chemicals most commonly employed for cleaning and disinfecting are sodium hypochlorite (NaClO), chlorhexidine (N,N″″1,6-Hexanediylbis[N′-(4-chlorophenyl)(imidodicarbon-imidic diamide)]) and EDTA, while calcium hydroxide (CaOH) is also used as an effective intra-canal medicament. These chemicals have to be supplemented with mechanical instrumentation to achieve bacterial elimination within the root canals. The primary limitation of current RCT methods is the inability of these chemicals to reach the anatomical complexities of the root canal.
Further, this method of bacterial elimination is not an instantaneous process and is found to be least effective in the anatomical complexities of the root canals. In the past, efforts were made to use higher concentrations of chemicals to achieve effective bacterial elimination. However, some of the perennial concerns were not examined. The effectiveness of these chemicals (such as root canal irrigants) at various depths inside the dentinal tubule is not clear. It has been demonstrated that the effective penetration of these chemicals into the dentinal tubules is limited, and therefore, bacteria remained viable at greater depths in the dentinal tubules at all levels in the root canal. Also, long-term use of such chemicals and medicaments can lead to the development of resistance to the chemicals and medicaments in the target organisms. Further, studies have shown that sodium hypochlorite reduces the modulus of elasticity and flexure strength of dentin structure, while saturated calcium hydroxide reduces the flexure strength of dentin. It has also been observed that some of the common root canal pathogens such as Enterococcus faecalis (E. faecalis) and Candida albicans (C. albicans) are resistant to calcium hydroxide.
Persistence of bacteria within the root canal dentin after root canal treatment is usually the main cause of failure of root canal treatment. Use of tetracycline has been found to effectively kill or destroy the bacteria. However, in most countries, tetracycline cannot be dispensed without a prescription. Thus, despite its effectiveness, the use of tetracycline was not a commercially viable option.
Recently, photodynamic therapy (PDT) has emerged as a promising treatment of cancer and other diseases utilizing activation of an external chemical agent, called a photosensitizer or PDT drug, by light. This drug is administered either intravenously or topically to the malignant site, as in the case of certain skin cancers. Subsequently, light of a specific wavelength, which can be absorbed by the PDT photosensitizer, is applied. The PDT drug absorbs this light producing a reactive oxygen species that can destroy the tumor. The photosensitizing compound is activated at a specific wavelength of light to destroy the target cell via a strong oxidizer, which causes cellular damage, membrane lysis and protein inactivation.
PDT relies on the greater affinity of the PDT drug for malignant cells. The light activation process of a PDT drug is initiated by the absorption of light to produce an excited singlet state (S1 or often written as 1P*, where P* represents the excited photosensitizer) which then populates a long-lived triplet state T1 (or 3P*) by intersystem crossing. It is the long-lived triplet state that predominantly generates the reactive oxygen species. Two types of processes have been proposed to produce reactive species that oxidize the cellular components (hence produce photooxidation) (Ochsner M, 1997).
Recent studies have shown that it is possible to kill bacteria, virus and fungi with low-power light/laser using the principles of photodynamic therapy (PDT) (Hamblin M R and Hasan T, 2004; O'Neill J F et al, 2002; Wainwright M, 1998; Jori G and Brown S B, 2004). PDT does not use a photothermal effect such as high powered lasers to eradicate bacteria. Therefore, PDT circumvents issues of thermal side effects in tissues. PDT has been used with relative success in the field of oncology for the treatment of neoplastic cells.
Different photosensitizers have been successfully demonstrated to have antibacterial property with their potential use in treating localized infections (Wainwright, M, 1998). Since the bactericidal activity of PDT is based on oxygen free radicals, the chance of microbes developing resistance is minimal compared to other strategies (Hamblin M R and Hasan T, 2004; Wainwright M and Crossley K B, 2004). Different photosensitizers have been successfully demonstrated to have antibacterial property with their potential use in treating localized infections (Wainwright M, 1998).
Since free radical generation is highly dependent on environmental conditions, the physicochemical environment existing at the site of application can influence the outcome of the treatment. Unlike the treatment of skin disease, the root canal has substantially no native oxygen. Hence, oxygen must be introduced into the root canal system. In US 2009/0287566 and US 2011/0027384, both of which are incorporated herein by reference, I described a more suitable photosensitizing composition that, as discussed below, can be further improved by either ultrasonic or sonic energy or agitation by increasing the rate of reactive oxygen release and subsequently the effectiveness of PDT. In addition, as discussed below, a micro-bubble solution, which is cationic or anionic, but preferable anionic, in nature, when activated with ultrasonic/sonic frequency or agitation will result in bubble (created by agitation)-bubble (in the solution) interaction and bubble-root canal wall interaction, which would facilitate the physical/mechanical effect of micro-bubbles. This physical/mechanical effect between micro-bubbles and root canal wall should significantly favor debridement and further enhance biofilm disruption. Meantime, an oxidizing agent (such as hydrogen peroxide) in the micro-bubble solution should interact with the organic debris within the root canal leading to the formation of oxygen, which allows the micro-bubbles to grow and propel towards the root canal wall (to further improve debridement). Finally, the presence of micro-bubbles in the solution should act as a scatterer, allowing light to penetrate laterally into the dentinal tubules/anatomical complexities of the root canal. Thus the solutions described therein appeared to provide excellent results in tests, a system for introducing the solutions into the root canal and activating the root canal is necessary.